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Background: IPI is a fully human monoclonal antibody that potentiates immune response by inhibiting CTLA-4. CA184-041 is a double-blind, randomized phase 2 study of IPI combination with P/C in chemotherapy- naïve recurrent/metastatic lung cancer. Methods: 204 pts were randomized 1:1:1 to receive: IPI + concurrent schedule (CON) IV P/C, IPI + phased schedule (PHA) P/C, or P/C alone (PBO). IPI was administered at 10 mg/kg q3wks starting with cycle (c) 1 x 4 (CON) or starting with c 3 x 4 (PHA) then q3mo. P/C was given as 175 mg/m² and AUC=6 q3wks x 6. Efficacy was assessed by immune-related response criteria (irRC) and mWHO. The primary endpoint compared immune-related PFS (irPFS) between CON vs PBO and PHA vs PBO. Results: Baseline characteristics were generally balanced. Table 1 presents final irPFS using irRC, final PFS using mWHO, interim OS, and ir best overall response rate (irBORR) using irRC. Final OS results will be presented. IPI + P/C was generally well tolerated. IPI did not increase P/C related toxicity. Total gr 3/4 irAEs (pruritis, rash, alopecia, diarrhea, colitis) were 20% and 15% for CON and PHA regimens, respectively; all resolved. Gr 5 toxic epidermal necrolysis was seen in 1 pt for CON. Conclusion: Ipilimumab in combination with P/C met its primary endpoint by demonstrating superiority in irPFS compared with P/C alone with consistent findings across other efficacy endpoints. The PHA regimen appeared to demonstrate better efficacy than the CON regimen. These results support further study of ipilimumab in NSCLC.